Improve markers for inline line-wrapped elements

If an inline line-wrapped element starts with a line break, its first
rect will have an area of almost zero. The marker used to end up on that
rect, seemingly on the line before the actual link, which was very
confusing. Now, such small areas are rounded to zero, and all
`visibleRects` that have a zero area are discarded, solving the problem.

An example can be found at the bottom of this page:
http://swrevisited.wordpress.com/esbr-facts/
Try points one pixel into the elements from the edges

On newyorker.com, `transform: translate3d(0, 0, 0)` is applied on the
content container, to force hardware acceleration. It seems to move
everything a pixel, causing `document.elementFromPoint` to fail at the
edges of elements. This commit no longer looks exactly at the edges of
elements, but one pixel in, which seems to be a safer strategy. (The
marker is still nicely placed exactly on the edge, though.)

Example page:
http://www.newyorker.com/currency-tag/the-virtual-moleskine